Grandpa never said as much, but I could tell he was disappointed when he saw (smelled) that I was smoking again. The old man is famous for remarking that a cigarette is a plug of tobacco rolled in paper with a fire at one end and a fool on the other.
He told me that peeling a dozen potatoes will take most stains off your hands (Grandpa was in the army) but nicotine requires lemon juice. Citric acid dissolves this evil tar better than any other common substance.
In this case however, use the white part of the lemon rind and rub that substance into the stained skin - then use a Brillo pad or SOS scrubbing pad and the stain will scrub right off.
Today, I still use lemon slices but the white part of the lemon peel, rubbed vigorously between my fingers and thumb, works the best. I follow this all natural treatment with a dry SOS pad and the combination of these two substances will clean ANY stain of my skin.